Hot nanoindentation of nanocrystalline Ni-W alloys

High-temperature nanoindentation experiments are conducted to assess the activation enthalpy for deformation of nanocrystalline Ni-W alloys, for grain sizes between 3 and 80 nm. Thermal softening becomes less pronounced at finer grain sizes, and the activation enthalpy has an apparent inflection at a grain size near ∼10-20 nm, in the vicinity of the Hall-Petch breakdown. This inflection is related to that observed in the activation volume for deformation, and is associated with a shift to grain boundary-mediated deformation at the finest grain sizes.